Titanium dioxide dielectric materials



Patented July 29, 1941 g I 2,424,853

umrao STATES PATENT OFFICE TITANIUM DIOXIDE DIELECTRIC 7 MATERIALS Moyer M. Saflord, Schenectady, N. Y., aasignor to General Electric Company, a corporation of New York No Drawing. Application May 0, 1944,, Serial No. 584,537

12 Claims. (Cl. 117-106) The present invention relates to improved ti- The following table show the electrical propertanium dioxide dielectric materials. It is parties of an untreated calcined titanium dioxide ticularly concerned with an improved titanium and 8. treated titanium dioxide obtained by treatdioxide filler for insulating compositions and with" ment with a methylchlorosilane mixture consistelectrically insulating compositions containing 5 ing essentially of trimethyl chlorosilane-silicon the same tetrachloride azeotrope and boiling between 51 In my Patent No. 2,106,039, I described the prodeg. and 64 deg. C. at atmospheric pressures. The duction of a, l i d tita iu di xid h -a electrical tests were made by molding mixtures of tcrized by a high dielectric constant and a low 7 parts of the calcined, 35-mesh titanium dioxide power fact r, Th mat rial as btainedby l with parts polystyrene in disks 200 mils thick heat-treating commercial titanium dioxide at a and 4 inches in diameterand determining the temperatureofat least about 1350 deg. C. dielectric constant, power factor and loss factor The present invention is based on my diseov- 0f the disks at 60 cycles as removed from the cry that a further andsubstantial improvement Dress nd h f r 0 h r in a 0 per cent in the electrical properties of calcined titanium h midity ch mber. dioxide may be obtained by treatment thereof with an organo-silicon halide, e. g. a methyl sili- Ohrs. 70 hrs. con halide or a mixture of such halides capable of rendering the treated material water-repellent.

Examples of organo-silicon halides suitable for 90 $53 the purposes of the present invention are given 161 in Patnode Patent 2,306,222 and include alkyl, 21 1 e. g., methyl, aryl, e. g.,'phenyl, alkaryl, e. g. 1108 tolyl, and aralwl, e. g.,' phenyl methyl silicon halides. I prefer to employ compositions comprising a methyl silicon halide or a mixtu r The marked increase in the dielectric constant methyl silicon halides, particularly compositions of the untreated sample is app rently due to the containing an azeotropic mixture of trimethylhigh dielectric constant of the water adsorbed chlorosilane and silicon tetrachloride such as are y the untreated titanium dioxide.

described in the copending application of rml- The treated titanium dioxide can be advantacis J. Norton, Serial No. 476,767, filed February geously employed as all or part of the insulating 22, 1943, and assigned to the same assignee as or dielectric material in various electrical applithe present invention. cations.

I have found that the treatment of calcined Dielectric sheets may be prepared by comtitanium dioxide with organo-silicon halides pref- 85 pounding-the treated powder with synthetic reserably containing an average of more than one inous compositions such as alkyd resins, polyand less than three organo groups attached to styrene, polythene. various synthetic rubbers, silicon produces a water-repellent dielectric maetc., and rolling or pressing the products into a teriai whose electrical properties are uniform, thin sheet. Mixtures of polystyrene and the substantially independent of changing humidity 40 treated titanium dioxide are particularly useful conditions, and generally superior under any where a high i le c constant. 8

.given conditions to those of untreated titanium terial is required. Such compositions which are dioxide. The treated material may be prepared, both moldable and machinabie may be made, for

for example,by agitating aflnely-divided calcined example, by mixing a benzene solution of polytitanium dioxide in a closed container filled with styrene with finely-divided treated titanium divapors of the treating material, followed by heatoxide and drying and molding the product. The ing of the treated material at deg. to 100 deg. titanium dioxide preferably comprises from 40 C. until there is no noticeable odor of hydrogen to per cent by weight of the mixture. The dichloride given oil. The amount of treating maelectric constant of these mixtures increases with terial depends upon the particular organo-silicon to increase in the titanium dioxide content. The halide employed. With methyl silicon halides or sheeted products are particularly useful as conmixtures thereof with silicon tetrachloride, I predenser dielectrics.

fer to use from one to ten per cent by weight of The treated titanium dioxide can also be used treating material basedv on the weight of the to advantage as a filler for various conductor intitanium dioxide. 66 sulatins compositions where high dielectric cona 3 stant and low power factor are required. The following compound is an example of cable insulating compound possessing such a combination of properties.

Per cent Polybutene 20 Cyclized rubber 13.6 Zinc stear 0.9 Treated titanium dioxide 85.0

The titanium dioxide used in this formula was prepared by firing a commercial powder at 1360 deg. C., grinding the product to 100 to 200 mesh, and treating the ground material with a mixture of methyl silicon chlorides. A cable insulated with this compound was flexible and had a dielectric constant of 8.2 and a power factor of 0.0006 at 46.4 megacycles. No change in the electrical loss characteristics of the insulating material was noted when the compound was subjected to 100 per cent humidity conditions for 50 hours.

Higher loadings than 65 per cent can be made in this type of compound by slight modification of the compound ratios. Furthermore the dielectric constant is not directly proportional to the per cent loading beyond 50 per cent, .but is more nearly logarithmic, so that for very little more loading a considerable increase in dielectric constant is noted. Thus it is possible to construct cable compounds having a wide range of dielectric constants.

Dielectric sheets for condenser and other uses comprising the treated titanium dioxide may ako be prepared by incorporating the treated powder into paper at the time the paper is being made. Papers comprising titanium dioxide and other fillers treated with organo-silicon halides are more fully described and claimed in my copending application S. N. 534,538, flied concurrently herewith and assigned to the same assignee as the present invention,

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Finely divided titanium dioxide which has been calcined at a temperature or at least about 1350 0., treated with vapors of a methyl silicon chloride mixture and thereafter heated at a t.- perature of from 60 to 100 C.

2. A dielectric material comprising titanium dioxide which has been calcined at a temperature of at least about 1350' C., treated with vapors of an organo-silicon halide capable of rendering the titanium dioxide water-repellent and thereafter heated at a temperature oi. from 60 to 100 C.

3. A dielectric material comprising titanium dioxide which has been calcined at a temperature of at least about 1350 C. and made water-repellent by contacting the calcined material with vapors of a methyl silicon chloride mixture having an average of at least one and less than three methyl groups attached to silicon atoms and thereafter heating the resultant product at a temperature of from 60 to 100 C.

4. A dielectric material comprising titanium dioxide which has been calcined at a temperature of at least about 1350' 0., treated with a mixture of at least two different methyl silicon chlorides and thereafter heated to a temperature of from 60 to 100 C.

5. An insulating material of high dielectric constant comprising a polystyrene-bonded mass of a titanium dioxide which has been calcined at a temperature of at least about 1350' 0., treated with vapors of a mixture of methyl silicon halides and thereafter heated to a temperature of from to 100 C. to render said titanium dioxide water-repellent.

0. A dielectric material consisting of a resinous binder comprising polystyrene and from 40 to per cent by weight of water-repellent calcined titanium dioxide produced by heating titanium dioxide at a temperature of at least about 1350' 0.. contacting the calcined material with a composition comprising an azeotropic mixture of trimethylchiorosilane and silicon tetrachloride and thereafter heating the product to a temperature of from 60 to C. s

'7. The process of producing a titanium dioxide having a low power factor which comprises calcining titanium dioxide at a temperature of at least about 1350 C.,treating the calcined product with vapors oi organo-sllicon halides containing an average of more than one and less than three organo groups attached to silicon and heating the treated product at a temperature of from 60 to 100 C.

8. The process of claim 7 wherein the organosilicon halides are methyl silicon chlorides.

9. The method which comprises treating titanium dioxide which has been calcined at a temperature of at least about 1350 C. with vapors of an organo-silicon halide capable of rendering the titanium dioxide water-repellent, and thereafter heating the vapor-treated material at a temperature of from 80 to 100 C.

10. The method which comprises treating flnely divided titanium dioxide which has been calcined at a temperature of at least about 1350' C. with vapors of a methyl silicon chloride mixture, and thereafter heating the vapor-treated material at a temperature of from 60 to 100 C.

11. An electrically insulating material comprising a polystyrene-bonded mass of titanium dioxide which has been calcined at a temperature of at least about 1350 C., treated with vapors of a methyl silicon chloride mixture having an average of at least one and less than three methyl roups attached to silicon atoms, and thereafter heated at a temperature of from 60 to 100 C.

12. A dielectric material comprising a polystyrene-bonded mass of titanium dioxide which has been calcined at a, temperature of at least about 1350 C.. treated with a mixture of at least two different methyl silicon chlorides, and thereager heated at a temperature of from 60 to 1 C.

MOYER M. BAP'I'ORD.

REFERENCES CITED The following reierences are of record in the iile of this patent:

UNITED STATES PATENTS 65 Number Name Date 2,279,762 Scott et al Apr. 14, 1942 2,300,222 Patnode Dec. 22, 1942 2,106,039 Saflord Jan. 18, 1938 

